I'm not sure which "fender mounted solenoid" you would be referring to.
Please download the PDF file HERE
The file will be deleted from the file server in a few days due to copyright restrictions, so you may want to save a copy to your computer for future reference.
The file contains the starting system wiring diagrams for your truck. You can see by these diagrams that the starter relay is located in the Battery Junction Box (BJB).
You can test the circuit from the relay to the starter by removing the relay and jumping across from pin 30 to pin 87 in the relay connector. If this works to make your starter kick in and crank, then either the relay itself is bad, or there is a problem with the "control side" of the relay.
If there is a problem on the control side of the relay, about all you can do is check continuity between the relay and the Powertrain Control Module (PCM) connector and check for power at Pin 87 to see if there is start voltage from the ignition switch.
If both of these are good, you could be having a problem with your security system (something like intermittently not recognizing your key) or there may be a problem with the PCM. These things will require interfacing with your onboard computer network with the proper equipment to diagnose.
Let me know if you need any more information or assistance.